would getting new pistons/rods in a 99 jdm ITr motor that would raise the compression to 12+ on stock bore yield any wortwhile gains if it was left on a stock head other then some bc4 cam's?

it would be on a jdm header as well. what kinda gains would there be from upgrading the pistons/rods/compression and cams? Im trying to see if it would be worthwhile or a waste because then i might need a full valvetrain assembly and better header to really get power out of it.